1. Field of the Invention
The present invention relates in general to differentials for automotive vehicles and more particularly to a slip control device for a differential.
2. Description of the Prior Art
A known slip control device for a differential includes a hydraulically operated friction clutch unit which is variably engaged for varying a differential action as disclosed in Japanese Provisional Patent Publication Nos. 62-103226 and 62-103227.
In order to retain a sufficient supply of a driving force to the driving wheels during cornering of the vehicle, it is desirable for the clutch unit to be engaged more strongly, i.e., it is desirable to increase a slip limiting force (i.e., a force supplied to the clutch unit to limit a slip thereof and therefore a differential action) during cornering of the vehicle.
The prior art slip control device is constructed, for example, so that a slip limiting force is determined by a curve radius and a centripetal acceleration of a cornering vehicle. While such a slip control device makes it possible to retain a sufficient supply of a driving force to the driving wheels and thereby improve the power supplying characteristic during cornering of the vehicle, it encounters problems in that the roll of the vehicle during power slide running thereof becomes so large and that when the cornering inside driving wheel (i.e., the driving wheel nearer to the center of the cornering curve than the other of the paired driving wheels) is caused to rotate at a speed larger than the cornering outside driving wheel (i.e., the driving wheel remoter from the center of the cornering curve than the other of the paired driving wheels) an excessive oversteer is caused, making it difficult to drive the vehicle safely.
That is, an understeer which is desirable from the safety driving point of view is obtained when the cornering inside driving wheel is not lifted above the ground to slip but held in contact with the ground together with the cornering outside driving wheel. However, when the cornering inside driving wheel is lifted to slip with a slip limiting force being largely maintained, a driving force distributed to the cornering outside driving wheel becomes considerably larger than that to the cornering inside driving wheel, thus causing an excessive oversteer.